<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <title>动态菜单栏</title>
  <style>
    .hidden { display: none; }
    #menu ul { list-style-type: none; padding-left: 20px; }
    #menu li { margin: 5px 0; }
  </style>
</head>
<body>

<h2>欢迎访问系统</h2>

<!-- 登录按钮 -->
<div id="login-section">
  <button onclick="login()">登录</button>
</div>

<!-- 菜单栏 -->
<div id="menu" class="hidden"></div>

<script src="app.js"></script>

</body>
</html>